> they cannot control for the willingness to respond to polls at all
Why not? If they poll the same question (e.g. political party) repeatedly (e.g. in many elections) eventually you could build some kind of model of which parties poll-answerers are more likely to skew towards, or how much they shift compared to non-answerers. Not fundamentally a different process from other ways of removing bias from polls.
Why not? If they poll the same question (e.g. political party) repeatedly (e.g. in many elections) eventually you could build some kind of model of which parties poll-answerers are more likely to skew towards, or how much they shift compared to non-answerers. Not fundamentally a different process from other ways of removing bias from polls.